1. Field of the Inventions
The present inventions relate to exhaust gas cooling systems, for example, liquid-cooled exhaust systems that allow the cooling liquid and exhaust gases to mix with each other.
2. Description of the Related Art
Some known exhaust gas cooling systems include an exhaust gas conduit having an exhaust gas passage through which exhaust gases discharged from an engine pass and a cooling water passage through which cooling water passes. Some of these systems are also designed to mix the cooling water and exhaust gases before they are discharged to the atmosphere. Some water vehicles, such as small planing boats, include such exhaust gas cooling systems. For example, Japanese Patent Document JP-A-Hei 8-53098 discloses a water vehicle having such an exhaust system and a propulsion system that draws water through a bottom opening and spouts the water rearwardly from a rear end thereof to generate the propulsion power propel the water vehicle on the water.
Some designs for exhaust gas cooling systems for water vehicles include an exhaust gas conduit (exhaust manifold) extending from an engine to a water-lock (muffler). The exhaust gas conduit is formed with a dual pipe, i.e., an inner tube disposed inside and an outer tube disposed outside.
The inner tube defines an exhaust gas passage through which exhaust gases pass. The inner tube and the outer tube together define a cooling water passage therebetween through which cooling water passes. The outer tube extends to the vicinity of the water-lock to be connected to the water-lock via a rubber tube. The inner tube extends into the interior of the water-lock. Thus, the exhaust gases flow through the inner tube into the water-lock, while the cooling water flows between the outer tube and the inner tube and also between the rubber tube and the inner tube and then is released into the water-lock. The exhaust gases and the cooling water are then mixed within the water-lock.
Because the exhaust gases and the cooling water are mixed within the water-lock, the cooling water can flow back into the engine through the inner tube of the exhaust gas conduit due to the effect of exhaust gas pulsations caused by the engine. Thus, in order to reduce such an effect from the exhaust gas pulsations, some designs include an extended exhaust gas conduit. For example, in some designs, the exhaust gas conduit extends from a side of the engine, to a front end of the engine, to the other side of the engine, then rearwardly along the other side of the engine toward the water-lock.